The present invention relates generally to dynamoelectric machines and, more particularly, to fractional horsepower motors having means for isolating vibrations caused by axial movement of a shaft and for providing a thrust bearing surface for such shaft.
The fractional horsepower electric motor art is relatively well developed and a need has been long recognized for limiting the end play of a rotatable shaft. The Thompson et al. U.S. Pat. No. 2,958,908 and Shaffer U.S. Pat. No. 2,912,290 (both of which are assigned to the assignee of the present invention) are indicative of two approaches that have been used hereinbefore and wherein a resilient member is utilized to determine or limit the end play of a rotatable shaft.
In one approach, as shown for example in Church U.S. Pat. No. 3,743,871 (which is assigned to the assignee of the present invention), shaft end play toward the pulley end of the shaft is controlled by a split locking ring that bears against a thrust washer that is sandwiched between the split ring and a sleeve type bearing. End play toward the opposite pulley end of the shaft may be limited by the shaft striking and bearing against the back wall of a lubricant reservoir.
With particular reference to U.S. Pat. No. 3,743,871, it is noted that for at least more than a year prior to the filing date of the present application, a flat thrust plate has been interposed between the interior back wall of an oil reservoir cover and the opposite pulley end of the shaft. Such plates have been formed of materials having suitable antifriction properties, one example of which is a material sold under the name NYLATRON by the Polymer Corporation of Reading, Pa.
While constructions of this type have provided a satisfactory thrust system in terms of limiting shaft end play and providing satisfactory motor life, we have now determined that objectionable noise levels sometimes exist during operation of such motors. The more objectionable noise emanating from such motors typically has a frequency of about 50 cycles per second and of about 120 cycles per second as a result of shaft pulsations. The frequency of these pulsations is in fact a function of the power supply frequency.
Motors of the particular type illustrated in the above referenced Church patent and in Wendt U.S. Pat. No. 3,500,087 are of a type frequently referred to as a "skeleton" or "side coil" type motor. Motors of this type frequently are found in household appliances of those types where any hidden source of noise may be particularly objectionable. For example, even though the noise generated by such motor is not necessarily indicative of a malfunction, or impending motor or appliance failure; the purchaser of a new household appliance may become concerned about such noises.
For example, motors of the skeleton type are often used to circulate air within the food storage compartment of household refrigerators. If a 50 cycle or 120 cycle noise became audible when the door to such compartment was opened, undue alarm on the part of the refrigerator owner might result.
It will be understood that similar situations can result when motors are applied to other end uses and, accordingly, it would be generally desirable to provide new and improved electric motors that would retain the proven performance and reliability characteristics of existing motor designs but, in which, noise caused by motor shaft excursions may be substantially reduced, if not eliminated.
Accordingly, it is an object of the present invention to provide new and improved dynamoelectric machines having improved vibration isolation and thrust bearing systems.
It is a more specific object of the present invention to provide such motors wherein the complexity of the motor is not increased and wherein existing production methods and equipment may continue to be utilized.
It is a still more specific object of the present invention to provide new and improved subfractional horsepower skeleton type motors having an end thrust and noise isolating plate that is substantially isolated from a noise transmitting wall of an oil reservoir cover.